Conventionally, a seat reclining device of this type disclosed in, for example, the patent document 1 has been known. The seat reclining device according to the patent document 1 includes a lower arm supported at a seat cushion side and having a pawl having an outer toothed portion at a tip end thereof and an upper arm rotatably supported by the lower arm and at the same time fixed to a seat back side, the upper arm being formed with an inner toothed portion engageable with the outer toothed portion of the pawl. The reclining angle of the seat back can be adjustable by varying the engagement position between the inner and outer toothed portions.
In the seat reclining device disclosed in the patent document 1, a lock mechanism is provided which includes a cam for locking the pawl relative to the lower arm. The cam disclosed in the patent document 1 includes two types of cams, i.e., a first cam (44) engaged with a hinge pin (31) directly connected to the operating handle and a circular shaped second cam (41) disposed between the first cam and the pawl and capable of making contact with the pawl and a guide wall of the lower arm. By the rotational locking operation of the first cam, the pawl is pressed outwardly in a radial direction through the second cam thereby to be engageable with the inner toothed portion of the upper arm. Since the second cam is disposed between the guide wall and the pawl side surface, the pawl can be pressed in a direction in which the pawl is engaged with the inner toothed portion and at the same time a gap between the guide wall and the pawl side surface can be eliminated.